1. Field of the Invention
The present invention relates to a magnetic recording medium which comprises a substrate such as a base film made of a polyester film, aluminum metal or a dram which is coated with a magnetic powder composition dispersing a magnetic powder in an organic binder.
2. Description of the Prior Arts
Heretofore, in the preparation of a magnetic recording medium such as a magnetic tape, a magnetic card and a magnetic disc, it has been studied to industrially prepare magnetic recording media by using an organic binder and a magnetic powder such as .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, cobalt ion-adsorbed or doped iron oxide or a metal oxide containing CrO.sub.2, Fe, Co, Fe-Co or Ni or a metallic acicular fine powder.
Recently, it has been required to give higher recording density of a signal required for a magnetic recording medium such as the recording density in a region of 1 .mu.m of the minimum recording wavelength as required by home VTR (video tape recorder) or high characteristic audio-cassette tape.
In order to satisfy such requirements, a magnetic powder having further fine size has been used for such fine particle dispersion type magnetic recording medium since the magnetic uniformity of the magnetic recording medium is improved by reducing a particle size of the magnetic powder so as to satisfy the requirement for the high density recording medium.
On the other hand, an organic binder having superior affinity to the magnetic fine powder is required depending upon reducing the particle size of the magnetic powder. It has been difficult to satisfy with the requirement by using the binder used in the conventional technology. The affinity of the organic binder to the magnetic powder relates to a dispersibility of the magnetic powder in the magnetic powder composition or membrane and it highly affects to a reliability and durability when it is used for the magnetic recording medium. The organic binders used in the conventional technology have not enough affinity and have not enough toughness as a mechanics of a polymer.